SI units of current

The SI unit of current I is the ampere (A). An ampere was first defined as the current flowing when a charge of 1 C (coulomb) passed per second through a perfect (i.e. resistance-free) conductor. The SI definition is more rigorous the ampbre is that constant current which, if maintained in two parallel conductors (each of negligible resistance) and placed in vacuo 1 m apart, produces a force between of exactly 2 x 10-7 N per metre of length . We will not employ this latter definition. 

One of the first things you need to know is the relationship between current and electrical charge. Electric current is a measurement of the rate of charge flow. It measures the amount of charge that passes a given point in a given amount of time. The SI unit of current is the ampere, abbreviated A, and is commonly shortened to the word amp. One ampere is described by the flow of one coulomb of charge per second. The formula for current is seen in Equation 18.7 ... 

The basic SI unit of current has been named in his honor, the -> ampere. 

According to Faraday s law, the amount of substance that undergoes oxidation-reduction reaction at the electrodes is directly proportional to the amount of electric current that the reaction is subjected to. Faraday constant is equal to the charge of one mol of electrons, and is numerically equal to 96500 coulombs. You probably remember coulombs from your physics undergraduate courses. The unit coulomb is related to the unit ampere (SI unit of current). 

In an electrolysis experiment, we generally measure the current that passes through an electrolytic cell in a given period of time. The SI unit of current is the ampere (A) defined as the amount of current corresponding to 1 coulomb of charge per second. 

Electric Current The SI unit of current is the ampere (symbol A). The ampere is defined as the current carried by two parallel, straight wires of infinite length and negligible cross section that yields a force of 2 X 10 newtons (or 2 X 10 kg m s ) when the wires are held exactly 1 m apart. 

Jan 22, 1775, Lyon, France - June 10,1836, Marseille, France) Much of his early education was based on the L Encyclopedie of d Alembert and Diderot, but his interest in physics and chemistry derived from reading the works of Lavoisier. In 1801 he became lecturer in Bourg, and in 1804 in Lyon. Later that year he moved to Paris, where he eventually became Professor at the ficole Polytechnique, and in 1826 at the College de France. In 1814 he became a member of the Academy. Ampere was one of the most important universal scientists of the 19 century. His scientific achievements concern mathematics, physics, and chemistry. He is recognized as one of the founders of electrodynamics, following the discovery of the effect of an electric current on a magnet by -> Orsted. The basic SI unit of current has been named in his honor, the -> ampere. 

The International System (SI) unit of current (/) is the ampere, named after the French mathematician and physicist Andr6-Marie Ampere (1775-1836) [3]. Note from Figure 2.5 that the electron flow is shown moving in the direction opposite to the current because the direction of current is defined as the flow of positive charge and thus moves in a direction opposite to the negatively charged electron flow (although this convention is not universal). 

Power, P, defiaed as the rate at which work is performed, is expressed ia terms of energy divided by time and is most commonly given in units of horsepower, as for the power suppHed by mechanical devices such as diesel engines, or in the SI units of watts, especially when measuring electrical power. One horsepower is equivalent to the amount of power needed to lift 33,000 pounds (14,982 kg) one foot (30.5 cm) in one minute. One watt is equivalent to the power required to perform one joule of work per second. In a simple direct-current circuit where potential is represented by E ... 

Analogies exist between electric and magnetic fields. The magnetic flux (4>) is analogous to electric current and has SI units of webers (see Table 2-36). The magnetic... 

Electrical units. The fundamental SI unit is the unit of current which is called the ampere (A), and which is defined as the constant current which, if maintained in two parallel rectilinear conductors of negligible cross-section and of infinite length and placed one metre apart in a vacuum, would produce between these conductors a force equal to 2 x 10 7 newton per metre length. 

The SI unit of power or radiant flux (symbolized by W) equal to one joule per second (or, meter per kilogram per second ). With respect to electric currents, the watt is the rate of work expressed by a current of one ampere and a potential difference of one volt. See Power Radiant Flux... 

SI units of measurement, used by scientists around the world, derive their name from the French Systeme International d Unites. Fundamental units (base units) from which all others are derived are defined in Table 1-1. Standards of length, mass, and time are the meter (m). kilogram (kg), and second (s), respectively. Temperature is measured in kelvins (K), amount of substance in moles (mol), and electric current in amperes (A). 

AMPERE PER METER (A/m). The magnetic field strength in the interior of an elongated uniformly wound solenoid which is excited with c, linear current, density m its winding of 1 ampere per meter of axial distance. (The SI unit of magnetic field strength.)... 

COULOMB (C). The quantify of electric charge which passes any cross section of a conductor in 1 second when the current is maintained constant at 1 ampere. (The SI unit of electric charge.)... 

HENRY (H). A unit of inductance. The inductance of a circuit in which a current of 1 ampere induces a flux linkage of 1 weber. (The SI unit of inductance.)... 

TESLA (T). A unit of magnetic flux density (magnetic induction). The magnetic flux density of a uniform field that produces a torque of 1 newton-meter on a plane current loop carrying 1 ampere and having a projected area of 1 square meter on the plane perpendicular to the field. T = N/A in. (The SI unit of magnetic flux density)... 

VOLT (V). A unit of voltage. The voltage between 2 points of a conducting wire earning a constant current of 1 ampere, when the power dissipated between these points is 1 watt. (The SI unit of voltage.)... 

VOLTAMPERE (VA). A unit of apparent pov>er. The apparent power at the port of entry of a single-phase two-wire circuit when the product of (a) the rms (root mean square) value in amperes of the current and (b) the rms value in volts of the voltage is equal to 1. (The SI unit of apparent power.)... 

On some occasions, protocols may involve SI units of time, electric current, thermodynamic temperature, or luminous intensity. These units are also base units of the SI. Traceability to SI can even refer to realizations of derived SI units, such as those for energy, pressure, and amount of electricity. Solubility per unit pressure may be quoted in (mol/m3)/(m-s2/kg) or in (mol/m3)/ Pa, but should not be written as moTs2/(m2-kg) [5, 20], that is not in reduced form relating to units of quantities not actually measured. 

The prefix multipliers increase or decrease the size of the base unit, so that it more conveniently describes the system being measured. The base units that we will be using are listed in Table 1.1. For the purists, it is not strictly correct to include liters as a base unit, because volume is derived from length, and thus the official SI unit of volume is the cubic meter (m3), which is derived from the length base unit, the meter. Chemists frequently express mass in units of grams, which is derived from the kilogram. There are three other SI base units (the mole, the candela, and the ampere). We will consider moles (amount of material) and amperes (electric current) in subsequent chapters. The candela is a unit of light intensity or luminosity and does not concern us at this point. 

Note in the above expression we recognized that the current is the rate of flowing charges, I = AQ/At. So, in general, the power consumed or dissipated by an electrical circuit is given by P = IV. The SI unit of power is the watt, so we see that a watt is related to an ampere and a volt by ... 

Alessandro Volta built the first battery in 1800 permitting future research and applications to have a source of continuous electrical current available. The SI unit of electric potential difference is named after him. 

Andre-Marie Ampere created a mathematical theory in the 1820s for magnetic fields and electric currents. The SI unit of electrical current is named after him. 

Napoleon s armies spread the system throughout continental Europe, but the British (and consequently the Americans) hung to the old English inch-pound-second system. From cgs the kilogram-meter-second (mks) system evolved, and finally SI (Systeme International d Unites) was bom from mks with the addition of units of current (ampere), temperature (kelvin), and brightness (candela). The International Temperature Scale is defined by 13.8033 K (triple point of equilibrium H2) 24.5561 K (triple point of Ne) and 1234.93 K (freezing temperature of Ag). 

Resistance — Electrical resistance is the property of a material to resist or oppose the flow of an electrical -> current. The SI unit of resistance is the ohm (given the Greek symbol Q). The reciprocal of resistance is -> conductance, measured in siemens (S). The resistance of a material determines the magnitude of -> current that flows for a given -> voltage applied across the material, as given by -> Ohms law, AE = I-R, where AE is the potential difference across the material measured in -> volts,... 

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